How the Zebra Got Its Stripes

Zebras may have evolved their striped coat to avoid blood-sucking flies.

By Jef Akst | February 9, 2012

WIKIMEDIA COMMONS, JOHN STORR

Many a fable and tale propose preposterous theories about how the zebra got its stripes, but now science has finally provided a possible answer. According to new research published in the Journal of Experimental Biology, zebras’ black-and-white coloration helps protect the equids from blood-sucking horseflies, which find the stripes unattractive.

It’s all about how light is reflected, Susanne Akesson from Lund University told BBC Nature. Akesson found that in the black and brown horses, the light that is reflected is horizontally polarized, which was very attractive to flies. "From a white coat, you get unpolarized light," she explained, which doesn’t adhere to a specific plane. This the flies find less attractive.

Given the flies’ penchant for dark coats, Akesson and her colleagues wondered how zebras might fare. They placed boards that were all black, all white, and black-and-white striped in a field , covered them with insect glue, then counted the number of flies that got stuck to each. Strikingly, the striped board that most closely represented a zebra’s stripes had the fewest flies. “That was a surprise because, in a striped pattern, you still have these dark areas that are reflecting horizontally polarized light,” Akesson told BBC. "But the narrower (and more zebra-like) the stripes, the less attractive they were to the flies."

The team also put the fly-glue on three differently colored 3-dimensional horse models. Once again, the striped model attracted the fewest flies.

But whether or not the flies are the true reason for the zebras’ stripes remains to be seen. "Above all, for this explanation to be true, the authors would have to show that tabanid fly bites are a major selection pressure on zebras, but not on horses and donkeys found elsewhere in the world... none of which are stripy," evolutionary biologist Matthew Cob of the University of Manchester told BBC. "My hunch is that there is not a single explanation and that many factors are involved in the zebra's stripes.

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Once again, an article implies there is a proactive adaptive mechanism whereby animals adapt.

I am willing, able, and eager to acknowledge and accept any evidence that such a mechanism exists or has existed.Â

To say that a species developed or evolved a morphology "because" that morphology was "needed" or "because" that morphology yields an advantage over (whatever) is to imply that mutations are reflexive and deliberate.

If the author of this article, or an editor, or any other person can direct me to literature in which a proative adaptive mechanism produces an evolutionary result, I would be enormously grateful for references I can consult to learn about it.

In reference to another article, "Peppered Moths Re-examined, by Cristina Luiggi, there is a caption referring to it which indicates, "The textbook example of Darwinian evolution is tested and confirmed."

I shall raise the question there of whether Charles Darwin asserted the existence of, or implied the existence of, a proactive adaptive mechanism in peppered moths.Â I read him as a student some four decades ago, at which time, as I can recall, I found neither any citing of evidence of the Lamarckian notion of transmission of acquired characteristics nor any citing of evidence of a proactive adaptive mechanism (by which I would mean a mechanism whereby an adaptive-appropriate mutation or a series of them is/are "selected" by members of a species to "deal with" a particular challenge in an environment, or to come up with the right mutation or the right set or series of mutations to achieve greater fitness -- such as to solve a problem threatening the survival of that species.

As to the peppered moth, and as to the so-called Darwin's finches, there is a profusion of rhetoric implying that individuals within these species "adapt" to certain kinds of changes in nature of food supply, or changes in their susceptibility to being more or less camouflaged in regard to certain predators.Â The hard data strike me as implying, in each such case, not new mutations but, rather, a variety of existing genes (or epigenetic propensities) whereby what is selected is on an either/or basis -- that is, as certain specific environmental changes occur the individuals with more copies of one gene are filtered for by the environmental selector, and when the specific environmental specific changes back to another selective state, the members of the species with more copies of another are selected for.Â If that is not quite the nature of the mechanism which allows two or more either/or types ofselection, I would be grateful for references to the micro-biological details.

As for zebras, there does not appear to be any either/or kind of mechanism at work, whereby zebras would -- if a certain predator were to "adapt" and begin to prefer to kill and eat striped individuals, would proactively adapt and begin being selected foranother external color scheme.

Again, I am ready, willing and able to acknowledge and accept any hard evidence, whatsoever, indicating that a species has the capability of proactively adapting, as opposed to merely coming up with a series of random mutations, one after another after another after another... in coming up with an enormously complex gene recipe that specializes.Â (As I have pointed out elsewhere, there are enormously long and complex transduction cascades involved in some of the thousands (millions?) ofvital physiological responses; and where even a single alteration in the order or nature of such a complex and elongated and series-dependent process gets out of whack, homeostasis is disrupted and the resulting alteration in physiological morphology in the vast preponderance of instances is deleterious to fitness, in fact in the order of perhaps thousands to one deleterious.

I welcome any specific references to hard data whereby Darwin's thinking on this issue (of what proactive adaptation-appropriate mutational direction occurs, or has occurred, in the peppered moth, in Galapagos finches, in zebras, or in any other species.Â And, if no such mechanism has been empirically established, then surely we would not wish such assertions to be implied, hundreds or thousands of times per year, in journals scientifically and professionally edited, nor in textbooks children are required to read, nor in any other source asserted to represent something about what is "good" science, versus what is mere (shudder) biased, metaphysical dogma.

Once again, an article implies there is a proactive adaptive mechanism whereby animals adapt.

I am willing, able, and eager to acknowledge and accept any evidence that such a mechanism exists or has existed.Â

To say that a species developed or evolved a morphology "because" that morphology was "needed" or "because" that morphology yields an advantage over (whatever) is to imply that mutations are reflexive and deliberate.

If the author of this article, or an editor, or any other person can direct me to literature in which a proative adaptive mechanism produces an evolutionary result, I would be enormously grateful for references I can consult to learn about it.

In reference to another article, "Peppered Moths Re-examined, by Cristina Luiggi, there is a caption referring to it which indicates, "The textbook example of Darwinian evolution is tested and confirmed."

I shall raise the question there of whether Charles Darwin asserted the existence of, or implied the existence of, a proactive adaptive mechanism in peppered moths.Â I read him as a student some four decades ago, at which time, as I can recall, I found neither any citing of evidence of the Lamarckian notion of transmission of acquired characteristics nor any citing of evidence of a proactive adaptive mechanism (by which I would mean a mechanism whereby an adaptive-appropriate mutation or a series of them is/are "selected" by members of a species to "deal with" a particular challenge in an environment, or to come up with the right mutation or the right set or series of mutations to achieve greater fitness -- such as to solve a problem threatening the survival of that species.

As to the peppered moth, and as to the so-called Darwin's finches, there is a profusion of rhetoric implying that individuals within these species "adapt" to certain kinds of changes in nature of food supply, or changes in their susceptibility to being more or less camouflaged in regard to certain predators.Â The hard data strike me as implying, in each such case, not new mutations but, rather, a variety of existing genes (or epigenetic propensities) whereby what is selected is on an either/or basis -- that is, as certain specific environmental changes occur the individuals with more copies of one gene are filtered for by the environmental selector, and when the specific environmental specific changes back to another selective state, the members of the species with more copies of another are selected for.Â If that is not quite the nature of the mechanism which allows two or more either/or types ofselection, I would be grateful for references to the micro-biological details.

As for zebras, there does not appear to be any either/or kind of mechanism at work, whereby zebras would -- if a certain predator were to "adapt" and begin to prefer to kill and eat striped individuals, would proactively adapt and begin being selected foranother external color scheme.

Again, I am ready, willing and able to acknowledge and accept any hard evidence, whatsoever, indicating that a species has the capability of proactively adapting, as opposed to merely coming up with a series of random mutations, one after another after another after another... in coming up with an enormously complex gene recipe that specializes.Â (As I have pointed out elsewhere, there are enormously long and complex transduction cascades involved in some of the thousands (millions?) ofvital physiological responses; and where even a single alteration in the order or nature of such a complex and elongated and series-dependent process gets out of whack, homeostasis is disrupted and the resulting alteration in physiological morphology in the vast preponderance of instances is deleterious to fitness, in fact in the order of perhaps thousands to one deleterious.

I welcome any specific references to hard data whereby Darwin's thinking on this issue (of what proactive adaptation-appropriate mutational direction occurs, or has occurred, in the peppered moth, in Galapagos finches, in zebras, or in any other species.Â And, if no such mechanism has been empirically established, then surely we would not wish such assertions to be implied, hundreds or thousands of times per year, in journals scientifically and professionally edited, nor in textbooks children are required to read, nor in any other source asserted to represent something about what is "good" science, versus what is mere (shudder) biased, metaphysical dogma.

Once again, an article implies there is a proactive adaptive mechanism whereby animals adapt.

I am willing, able, and eager to acknowledge and accept any evidence that such a mechanism exists or has existed.Â

To say that a species developed or evolved a morphology "because" that morphology was "needed" or "because" that morphology yields an advantage over (whatever) is to imply that mutations are reflexive and deliberate.

If the author of this article, or an editor, or any other person can direct me to literature in which a proative adaptive mechanism produces an evolutionary result, I would be enormously grateful for references I can consult to learn about it.

In reference to another article, "Peppered Moths Re-examined, by Cristina Luiggi, there is a caption referring to it which indicates, "The textbook example of Darwinian evolution is tested and confirmed."

I shall raise the question there of whether Charles Darwin asserted the existence of, or implied the existence of, a proactive adaptive mechanism in peppered moths.Â I read him as a student some four decades ago, at which time, as I can recall, I found neither any citing of evidence of the Lamarckian notion of transmission of acquired characteristics nor any citing of evidence of a proactive adaptive mechanism (by which I would mean a mechanism whereby an adaptive-appropriate mutation or a series of them is/are "selected" by members of a species to "deal with" a particular challenge in an environment, or to come up with the right mutation or the right set or series of mutations to achieve greater fitness -- such as to solve a problem threatening the survival of that species.

As to the peppered moth, and as to the so-called Darwin's finches, there is a profusion of rhetoric implying that individuals within these species "adapt" to certain kinds of changes in nature of food supply, or changes in their susceptibility to being more or less camouflaged in regard to certain predators.Â The hard data strike me as implying, in each such case, not new mutations but, rather, a variety of existing genes (or epigenetic propensities) whereby what is selected is on an either/or basis -- that is, as certain specific environmental changes occur the individuals with more copies of one gene are filtered for by the environmental selector, and when the specific environmental specific changes back to another selective state, the members of the species with more copies of another are selected for.Â If that is not quite the nature of the mechanism which allows two or more either/or types ofselection, I would be grateful for references to the micro-biological details.

As for zebras, there does not appear to be any either/or kind of mechanism at work, whereby zebras would -- if a certain predator were to "adapt" and begin to prefer to kill and eat striped individuals, would proactively adapt and begin being selected foranother external color scheme.

Again, I am ready, willing and able to acknowledge and accept any hard evidence, whatsoever, indicating that a species has the capability of proactively adapting, as opposed to merely coming up with a series of random mutations, one after another after another after another... in coming up with an enormously complex gene recipe that specializes.Â (As I have pointed out elsewhere, there are enormously long and complex transduction cascades involved in some of the thousands (millions?) ofvital physiological responses; and where even a single alteration in the order or nature of such a complex and elongated and series-dependent process gets out of whack, homeostasis is disrupted and the resulting alteration in physiological morphology in the vast preponderance of instances is deleterious to fitness, in fact in the order of perhaps thousands to one deleterious.

I welcome any specific references to hard data whereby Darwin's thinking on this issue (of what proactive adaptation-appropriate mutational direction occurs, or has occurred, in the peppered moth, in Galapagos finches, in zebras, or in any other species.Â And, if no such mechanism has been empirically established, then surely we would not wish such assertions to be implied, hundreds or thousands of times per year, in journals scientifically and professionally edited, nor in textbooks children are required to read, nor in any other source asserted to represent something about what is "good" science, versus what is mere (shudder) biased, metaphysical dogma.

In response to "keepitlegal's" comment, may I be more concise? As I understand the kernel of Darwinian evolution, it is that species evolve through "random mutation" and "natural selection" and not "a proactive adaptive mechanism." To speak as though evolution was the result of an organism's intentional efforts to adapt to an environment is, at best, sloppy scientific writing and may even imply some Creationist ideology.

The question of Lamarckian inheritance is slightly more subtle. It is true that the Stalinist option which kept Lysenko in business for decades, at hideous cost to Soviet peoples and to Darwinian biologists in the USSR, is thoroughly discredited (Paul Kammerer's "mid-wife toads" notwithstanding). Current studies of the epigenome, however, have seemingly brought "the inherence of acquired characteristics" back a step from the brink of "intelligent design" (or, perhaps, "purposive adaptation").

I would be fascinated to learn whether Darwin's original formulation (elaborated at the outset before Mendel's experiments were widely known and certainly before "genetics" could have come to Darwin's attention)Â is, indeed, about to be "modified" in light of a better understanding of genetic inheritance.

In response to "keepitlegal's" comment, may I be more concise? As I understand the kernel of Darwinian evolution, it is that species evolve through "random mutation" and "natural selection" and not "a proactive adaptive mechanism." To speak as though evolution was the result of an organism's intentional efforts to adapt to an environment is, at best, sloppy scientific writing and may even imply some Creationist ideology.

The question of Lamarckian inheritance is slightly more subtle. It is true that the Stalinist option which kept Lysenko in business for decades, at hideous cost to Soviet peoples and to Darwinian biologists in the USSR, is thoroughly discredited (Paul Kammerer's "mid-wife toads" notwithstanding). Current studies of the epigenome, however, have seemingly brought "the inherence of acquired characteristics" back a step from the brink of "intelligent design" (or, perhaps, "purposive adaptation").

I would be fascinated to learn whether Darwin's original formulation (elaborated at the outset before Mendel's experiments were widely known and certainly before "genetics" could have come to Darwin's attention)Â is, indeed, about to be "modified" in light of a better understanding of genetic inheritance.

In response to "keepitlegal's" comment, may I be more concise? As I understand the kernel of Darwinian evolution, it is that species evolve through "random mutation" and "natural selection" and not "a proactive adaptive mechanism." To speak as though evolution was the result of an organism's intentional efforts to adapt to an environment is, at best, sloppy scientific writing and may even imply some Creationist ideology.

The question of Lamarckian inheritance is slightly more subtle. It is true that the Stalinist option which kept Lysenko in business for decades, at hideous cost to Soviet peoples and to Darwinian biologists in the USSR, is thoroughly discredited (Paul Kammerer's "mid-wife toads" notwithstanding). Current studies of the epigenome, however, have seemingly brought "the inherence of acquired characteristics" back a step from the brink of "intelligent design" (or, perhaps, "purposive adaptation").

I would be fascinated to learn whether Darwin's original formulation (elaborated at the outset before Mendel's experiments were widely known and certainly before "genetics" could have come to Darwin's attention)Â is, indeed, about to be "modified" in light of a better understanding of genetic inheritance.

I noticed that the trials with the artificial zebras were in a field that did not appear to be in Africa (see images on BBC website). Can this research be considered valid if the field studies were not conducted in the correct biome?

I noticed that the trials with the artificial zebras were in a field that did not appear to be in Africa (see images on BBC website). Can this research be considered valid if the field studies were not conducted in the correct biome?

I noticed that the trials with the artificial zebras were in a field that did not appear to be in Africa (see images on BBC website). Can this research be considered valid if the field studies were not conducted in the correct biome?

It is amusing to see how we color our perception of biology with the bias of our experiences. Â Purposeful action in preparation for an encounter with an alien environment is the human way. Â I put on a jacket before going outside in the winter, or build an air-tight space capsule before riding my rocket into space. Â As pointed out by keepitlegal, nature works by conducting random experiments on randomly-generated diversity and takes on into the future what happens to survive. Â Millions of tries, over millions of years. Â We should, in the context of discussions of evolution, remember that nature does not operate on a humanly intelligible time scale. Â Nature has patience, we do, apparently, not.

It is amusing to see how we color our perception of biology with the bias of our experiences. Â Purposeful action in preparation for an encounter with an alien environment is the human way. Â I put on a jacket before going outside in the winter, or build an air-tight space capsule before riding my rocket into space. Â As pointed out by keepitlegal, nature works by conducting random experiments on randomly-generated diversity and takes on into the future what happens to survive. Â Millions of tries, over millions of years. Â We should, in the context of discussions of evolution, remember that nature does not operate on a humanly intelligible time scale. Â Nature has patience, we do, apparently, not.

It is amusing to see how we color our perception of biology with the bias of our experiences. Â Purposeful action in preparation for an encounter with an alien environment is the human way. Â I put on a jacket before going outside in the winter, or build an air-tight space capsule before riding my rocket into space. Â As pointed out by keepitlegal, nature works by conducting random experiments on randomly-generated diversity and takes on into the future what happens to survive. Â Millions of tries, over millions of years. Â We should, in the context of discussions of evolution, remember that nature does not operate on a humanly intelligible time scale. Â Nature has patience, we do, apparently, not.

The question of Lamarckian inheritance is slightly more subtle. It is true that the Stalinist option which kept Lysenko in business for decades, at hideous cost to Soviet peoples and to Darwinian biologists in the USSR, is thoroughly discredited (Paul Kammerer's "mid-wife toads" notwithstanding). Current studies of the epigenome, however, have seemingly brought "the inherence of acquired characteristics" back a step from the brink of "intelligent design" (or, perhaps, "purposive adaptation").Â

The question of Lamarckian inheritance is slightly more subtle. It is true that the Stalinist option which kept Lysenko in business for decades, at hideous cost to Soviet peoples and to Darwinian biologists in the USSR, is thoroughly discredited (Paul Kammerer's "mid-wife toads" notwithstanding). Current studies of the epigenome, however, have seemingly brought "the inherence of acquired characteristics" back a step from the brink of "intelligent design" (or, perhaps, "purposive adaptation").Â

The question of Lamarckian inheritance is slightly more subtle. It is true that the Stalinist option which kept Lysenko in business for decades, at hideous cost to Soviet peoples and to Darwinian biologists in the USSR, is thoroughly discredited (Paul Kammerer's "mid-wife toads" notwithstanding). Current studies of the epigenome, however, have seemingly brought "the inherence of acquired characteristics" back a step from the brink of "intelligent design" (or, perhaps, "purposive adaptation").Â